Observation of eight-photon entanglement

The creation of increasingly large multipartite entangled states is not only a fundamental scientific endeavour in itself 1 , 2 , 3 , but is also the enabling technology for quantum information 4 , 5 . Tremendous experimental effort has been devoted to generating multiparticle entanglement with a growing number of qubits 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 . So far, up to six spatially separated single photons 10 , 11 , 12 , 13 , 14 have been entangled based on parametric downconversion 17 . Multiple degrees of freedom of a single photon have been exploited to generate forms of hyper-entangled states 18 , 19 . Here, using new ultra-bright sources of entangled photon pairs 20 , an eight-photon interferometer and post-selection detection, we demonstrate for the first time the creation of an eight-photon Schrödinger cat state 1 with genuine multipartite entanglement. The ability to control eight individual photons represents a step towards optical quantum computation, and will enable new experiments on, for example, quantum simulation 21 , 22 , topological error correction 23 and testing entanglement dynamics under decoherence 24 . Researchers demonstrate the creation of an eight-photon Schrödinger-cat state with genuine multipartite entanglement by developing noise-reduction multiphoton interferometer and post-selection detection. The ability to control eight individual photons will enable new multiphoton entanglement experiments in previously inaccessible parameter regimes.